Electromagnetic brake



- 'July 18,1944. CQ'SJANES 2,353,900

ELECTROMAGNETIC BRAKE Filed Sept. 19, 1942 INVENTOR. BY (lg/don 1S.Lia/mes Patented July 18, 1944 ELECTROMAGNETIC BRAKE Clinton S. Janes,Elmira Heights, N. 1., minor to Bendix Aviation Co poration, South Bend,Ind., a corporation of Delaware Application September 19, 1942, SerialNo. 458,973

6 Claims. (Cl. zoo-as) The present invention relates to anelectromagnetic brake for motors and" more particularly to anarrangement for automatically arresting the rotation of an enginestarting motor when the starting switch is opened.

In electrical starters for internal combustion engines of the type inwhich a pinion is projected into mesh with an engine gear by the initialacceleration of the starting motor, and is thrown out of mesh when theengine starts, it is desirable to have the starting motor stop quicklywhen it is de-energized so that it it be start, and the consequentkinetic energy which must be transmitted to the engine may bedestructive to the starter drive. This hazard is particularly serious inheavy duty-installations where the rotating parts are heavy, and thedrive is usually operating close to the limit of its safe load capacity.

Moreover, in those forms 0! starter drive in which the demeshingoi'thepinion is aided or eflected by the deceleration of the startin motorwhen it is de-energized, some form of braking means for the startingmotor is often desirable to assist the demeshing action, such forinstance as shown in the patents to Loehr et al., 2,135,620, or Janes,2,167,891.

It is an object of the present invention to provide a novel automaticelectrical braking arrangement for motors which is eilicientand reliablein operation and simple and economical ,in- 9Qmn- ,Q

It is another'bbiect to provide such a device which secures the brakingeflect by maintaining or strengthening the fleld of the starting motorwhile reducing or stopping the flow of current from the battery throughthe armature.

It is another object to provide such a device in which the brakingeflect is secured by short-circuiting the armature either partially orcompletely.

It is another object to provide such a device which is automaticallybrought into action by the opening of the starting switch.

in which the braking eflect is removed as soon as the starting motorcomes substantially to rest.

It is another object to provide such a device including means formaintaining the braking eilect for a predetermined time after thestarting switch is opened.

Further objects and advantages will be apparent from the followingdescription taken in connection with the accompanying drawing, in which:

Fig. l is a diagrammatic representation of a starting system showing apreferred embodiment of the present invention;

Fig. 2 is a similar view of such an arrangement in which thebrake-applying magneto switch is also used as the remote controlledstarting switch; and

Fig. 3 is a similar view of an embodiment of the invention incorporatinga positive time delay mechanism which maintains the braking eflect for ameasured interval of time.

In Fig. 1 01' the drawing there is illustrated a starting circuitcomprising a battery 1 grounded at 2 and connected by a lead 3 to astarting switch 4. Switch 4 is connected by a lead 5 to a conventionaltype or series wound starting motor com-prising a pair of field coils land I, an armature having a commutator 8,

"and two sets of commutator brushes 9, ii and II, II, brushes 9 and Iibeing connected to the field coils I and 1 respectively, and brushes i2and I! being grounded to complete the starting circuit.

A shunt circuit around the starting switch 4 is provided comprising alead I, a resistor i5 and a magnetic switch it. The value of theresistance It is not at all critical, but may conveniently be such thatwhen the starting switch 4 is open and the battery is connected to thestarting motor through the shunt circuit, the

yoltage drop through the resistor i5 will be a substantial fraction ofthe battery voltage. Means for closing the switch i6 during rotation ofthe starting motor and for holding it closed until the starting motorcomes substantially to rest is provided in the form of a coil ilconnected at one end by a lead it to the junction I! between-the fieldcoil 1 and brush ILzthe opposite end of coil I! being grounded at Inthis embodiment oi the invention, the electromagnetic "braking eflect issecured by grounding the Junction between field coil 6 and brush I whenthe starting switch 4 is opened,

It is another object to provide such a device thus increasing thecurrent flow through said field coil and at the same time shortcircuiting that part of the armature which is served by the brush 9. Ashere shown, this is accomplished by means of an electromagnetic switch22 connected by a lead 2| with the junction 24 between field coil 6 andbrush 9, and connected by a lead 25 to the ground. Grounding switch 22is provided with an actuating coll 2| which is arranged to close saidswitch responsive to opening of the starting switch 4. This is broughtabout by connecting the coil 2| in shunt with the resistor ,l! by meansof leads 21 and 28 so that the voltage drop across the resistor i isimpressed on said coil.

In the operation of this embodiment of the invention, starting with theparts in the positions illustrated, closure of the starting switch 4 bythe operator completes the starting circuit in the usual manner wherebythe motor is energized by the battery to rotate and perform its crankingoperation. When the armature oi the starting motor rotates, acounter-electromotive force is generated therein causing a substantialvoltage to be built up between the brushes and II and the groundedbrushes l2, The potential of the brush ii is impressed on the ccoil I!of magnetic switch l6 by means of the connection whereby said switch isclosed, thus closing the shunt circuit through resistor although nocurrent flows therethrough so long as the starting switch 4 is heldclosed.

When the engine starts, the operator opens the starting switch 4,whereupon the battery current is caused to flow through the shuntcircuit including resistor i5 and switch II. The consequent voltage dropacross the resistor I! is impressed on the coil 26 of the groundingswitch 22, causing it to close, thus groundinrthe field coil and shortcircuiting the armature through the brush 9. The field coil isconsequently strengthened by the removal of the counterE. M. I". of thearmature therefrom, and at the same time a current caused by the counterE. M. l". or the armature is permitted to flow throughthe circuitcomprising brush 9, connection 2|, switch, ground connection 25 and thegrounded brushes l2, l8. This current is in a direction to causereversal oi the rotation of the armature and thus quickly arrest itsforward rotation.

When the armature comes substantially to-rest, the counter E. M. F. ofthe armature disappears and the brush consequently is at approximate- 1yground potential. The 0011 I1 oi shunt switch i6 is thus de-energized,thereby permitting said switch to open. The shunt circuit being thusbroken, coil 2| oi the grounding switch I! is de-energized, permittingsaid switch to open, placing the starting mechanism in condition forre-actuation.

It will be noted that the resistor ll performs two functions. Itprovides a potential ior controlling the operation of the groundingswitch 22, and it also serves to limit the fiow or current through thefield coil 0, when grounded, to prevent overheating.

In the embodiment of the invention illustrated in Fig. 2 the magneticgrounding switch is caused to serve double duty as aremoteecontrolledstarting switch. As there shown, a battery |lgroundedatflisconnectedbyaleadlltoastarting switch contact 34. Acorresponding switch contact II is connected by a lead to a series-woundstarting motor comprising parallel field coils 81 and commutator brushes4| connected to the fields respectively, and brushes 4!, 4| grounded tocomplete the starting circuit. Means for connectingcontacts|4,||toclosethestartiu 2,sse,ooo

circuit is provided in the form of a bridging contact 44 actuated byacoil 4| grounded at one end at 4| and connected at the other endthrough lead 41 and push button 4| to the battery lead It will beunderstood that the push button 4| will be located conveniently to theoperator to provide a remote control oi the starting operation.

A shunt circuit around the starting contacts N is provided comprising amagnetic switch 4| and a resistor II, which are arranged to connect thebattery lead N with the starting motor lead 3|. Switch 4| is providedwith a coil '2, one end of which is grounded at U and the other endconnected by a lead 54 to the Junction 5! between the field coil 3| andarmature brush 4|, whereby said coil is energized by voltagecorresponding to the counter E M. F. .of the armature when it is inrotation.

Means for grounding the field coil I1 and short circuiting the armaturethrough the brush is provided, comprising a grounding switch contact llconnected by a lead 51 to the junction ll between the field coil andbrush and a contact 5| grounded at 6|. Contacts II, I! are positioned soas to be normally connected by the bridging contact 44, this engagementbeing maintained by suitable means such as a spring H.

In the operation of this embodiment of the invention, closure of thepush button 4| by the operator causes energization of coil 4| whichmoves the bridging contact 44 out of engagement with the groundingcontacts N and into engagement with the starting switch contacts |4, ll.The starting motor is thereby energized to cause the engine to becranked in the usual manner. When the armature rotates, the counter E.M. F. thereof is impressed on the coil I! of shunt switch 4| by virtueof the connection 4 to brush 4|, causing said switch to close and com-.plete the shunt circuit around the starting switch.

when the engine starts, the operator releases the push button 4|,thereby disconnecting contacts M, II and closing the ground connectionthrough contacts thus grounding the field coil |l as the operation ofthe grounding switch is eoncerned, it may be omitted altogether and theshunt switch 4| connected directly with the bat-, tery lead 3|. In suchcase, however, the braking efiect may be undesirably energetic. and thefield coil I1 and grounding contacts 44, may become over-heated altercontinued repetitious operation of the starter. It is preferredtherefore to retainithe resistor ll simply for the purpose of preventingoverloading of the field coil and contacts.

Fig. 3 shows the utilization oi a positive form 01 time delay mechanismfor maintaining the electromagnetic braking efiect for a predeterminedtime after opening the starting switch. Inthisfigure a battery llgrounded at I: is connected by a lead H to a starting switch II. Switch14 is connected by a lead II to the usual starting motor comprisingparallel field coils 1| and I1, commutator brushes II and II connectedto said field coils, and groimded commutator brushes and I2.

A shunt circuit around the starting switch I8 is provided comprising alead 88, a resistor 88 and a shunt magnetic .switch 88 having anactuating coil 88. One end of coil 88 is grounded at 81 and the otherend is connected through a resistor 88 to the starting motor lead l8.value of resistor 88 is not critical but is preterably oi the same orderas the resistance of the coil 88. C011 88 is designed to close switch 88when actuated by battery current flowing through resistor 88. v Q

Means for grounding both oi the field coils l8, l1, and completelyshort-circuiting the armature through both brushes I8, 18 is provided inthe form of a grounding switch 88 connected by leads 88, 8| and 82 tothe junction points 88 and 88 between the field coils I8, I! and brushesI8, 18 respectively and connected to the ground through a lead 88..Grounding switch 88 is provided with an actuating coil 88 which isenergized by the voltage drop across the resistor 88 by virtue ofconnections 81, 88.

Means are provided for opening switch 88 a predetermined time after thestarting switch 18 is opened. As here shown this means comprises a fixedcontact 88 connected by a lead IM to one The the bob I 88 of reed I88,setting the reed in vibra- 7 tion. After a period of time predeterminedby necessarily energetic, the operation of the deend of the coil 88, anda movable contact I82 connected by a lead I88 to the opposite end ofsaid coil, contact I82 being mounted on a flexible reed I88 anchored atI88 and provided with a weighted bob I88 on its free end whereby whenthe bob is flicked, the reed will vibrate for a predetermined timebefore permitting the contact I82 to come to rest against the contact88. Means are provided for opening contacts I82, 88, dur-' ing thecranking operation comprising a solenoid I81. grounded at one end at I88and connected at the other end by a lead I88 to the Junctions of thefield coils I8, TI and commutator brushes 18, I8 through leads 8|, 82. Aplunger II8 arranged to be actuated by the solenoid I81 is connected toa lever III pivoted at H2 and having a roller M3 on its free end inposition to engage the bob I88 of the vibrator reed I 88 and bend thereed back to open contacts I82, 88.

, In operation, with the partsin the positions illustrated, closure ofthe starting switch 18 completes the starting circuit through the motorcausing it to crank the engine in the usual manner. Closure of thestarting switch also completes a circuit to the ground through resistor88, lead I83, contacts I82, 88 and lead-|8I.

when the armature oi the motor rotates, the counter E. M. F. thusgenerated is impressed upon the solenoid I81 by virtue oi connections8|, 82, I88, thus causing plunger II8 to move the lever III to opencontacts 88, I82. Thereupon the 001188 of the shunt switch. 88 isenergized by vice may be rendered less drastic by omitting one of saidground connections 8| or 82 without otherwise ailecting the operation ofthe braking system.

While the operation of a-vibrator type time delay to retard closure of aswitch is old, as shown for instance in the patent to Loehr et 9.1..12,904, the use oi such a mechanism to delay the opening of a switch isbelieved to be novel. Applicant's understanding of the theory ofoperation in this case is as follows: When the contacts I82,, 88 areopened, thus removing the short circuit around the coil 88, the coilbecomes energized by the current traversing the resistor 88, thusbuilding up a magnetic field around the coil until the flow of currentthrough the coil reaches a substantially constant value, and themagnetic circuit thereof is substantially saturated. The inductivereactance of the coil is therefore very low, and practically the onlyresistance to the flow 0! current through said eoil'is now its pureohmic resistance. When the plunger H8 of solenoid I81 is released, thusflicking the reed I88, the fluttering of the contacts I82, 88 producesthe eilect oi an intermittent current applied to the coil 88 during theintervals when the con- 40 tacts are open. Since as above pointed out,the

the current flowing through the resistor 88 to cause closure of saidswitch.

When the engine starts, the starting switch 18 is opened by the operatorwhereupon the current to the starting motor is forced to traverse theshunt circuit including resistor 88 and shunt switch 85. The consequentvoltage drop across the resistor 84 is impressed on the coil 88 of thegrounding switch 88, thus causing said switch to close and ground thefield coils .18, "and short-circuit the armature by connecting both thebrushes 18, [8 to the ground. Closure of the grounding switch 88 alsogrounds and de-energi zes the solenoid I81 which releases the plungerIII), permitting the lever III to return to its idle position bysuitable means such as a spring I I8. 'I'his'return motion oi the leverII I flicks coil has very little reactance, this pulsating currenttraverses it freely, and the self-inductance of said coil smooths outthese pulsations into a substantially continuous current flow throughthe coil which accordingly maintains the magnetic field until thecontacts 88, I82 come to rest in engagement. Then the coil 88 isshort-circuited and de-energized and the shunt switch 88 permitted toopen.

Whether or not this is the precisely correct theory of operation of thedevice is believed to be immaterial, since the operation thereof hasbeen carefully observed and has been found to take place as described inthe statement of operation above set forth.

The device as at present constructed utilizes a non-inductive resistoras the resistance 88, by virtue 01' its economy and convenience, and noundue amount of sparking at contacts 88, I82 has been observed.Obviously an inductive resistor 88 would be still more efllcient.

While certain embodiments of the invention have been shown and describedin detail, it will be understood that other embodiments are possible andthat various changes may be made in the design and arrangement of theparts without departing from the spirit 0! the invention as deof saidarmature during rotation of the starting motor, and means actuated bythe voltage drop across the resistor when the starting switch is opened,operative to short-circuit the armature.

2. In combination with a starting circuit including a battery, astarting switch and a starting motor having a field and an armature,means responsive to opening of the starting switch for diverting thefiow oi battery current from the armature while maintaining said'fiowthrough the field, and means for opening the starting circult when thestarting motor comes substantially to rest.

3. In combination with a starting circuit including a battery, astarting switch and a starting motor having a field and an armature,means responsive to opening the starting switch for short circuiting thearmature while maintaining a connection from the battery through thefield of the motor, and means for breaking said connection after a timedelay sufficient to allow the armature to come substantially to rest.

4. In an engine starter a starting circuit including a motor and aswitch, closure 01' which causes energization of the motor to crank theengine, and means responsive to opening of the switch for shortcircuiting the armature oi the motor while maintaining a connection fromthe battery through the field ot the motor.

5. In an engine starter a starting circuit including a motor having afield and armature connected in series, and a double-throw magneticswitch normally short-circuiting the armature. manually operable meansfor energizing the switch to open the short-circuit and to close thestarting circuit, and means including a second magnetic switch energizedby the counter E. M. 1". of the armature for maintaining the startingcircuit closed aiter de-energization oi the first switch until thearmature comes substantially to rest.

6. In an engine starter a starting circuit including a battery, astarting switch and a serieswound motor having parallel fields andparallel commutator brushes, one set or brushes being connected to thefield coils and the other set being grounded to complete the startingcircuit; a circuit in shunt with the starting switch comprising aresistor and a magnetic switch having a coil, one end 01' which isgrounded and the other end connected to the junction of one field coilwith its connected commutator brush, and a second magnetic switcharranged when closed, to ground the Junction of another field coil withits connected commutator brush, and having an actuating coil connectedin shunt with said resister.

CLINTON S. JANES.

